Transformer core construction



Feb. 27, 19 2 A. E. FEINBERG ETAL TRANSFORMER CORE CONSTRUCTION Original Filed Jan. 10, 1956 2 Sheets-Sheet 1 1962 A. E. FEINBERG ETAL 3,

TRANSFORMER CORE CONSTRUCTION Original Filed Jan. 10, 1956 2 Sheets-Sheet 2 1 N Q N @lvez/z orrg rates nite This invention relates generally to electro-magnetic devices such as the transformers of apparatus for igniting and operating gaseous discharge devices. Particularly the invention is concerned with the structure of the core and laminations making up such transformers.

This is a divisional application of application for patent of Albert E. Feinberg et al., Serial No. 558,236 filed January 10, 1956.

The shell type of transformer core is desirable from many standpoints. It is easy to assemble, compact, results in a quiet transformer, and usually provides at least one complete unbroken magnetic circuit in the frame. By reference to the designation shell type it is intended to designate a type of core structure in which there is a usually elongate rectangular outer frame member having parallel elongate side parts bridged at their ends by short bridging portions maintaining the spacing across the narrow dimension of the frame member. A central winding leg extends along the core, being matingly engaged at its ends with the respective bridging portions. The side parts have windows punched on opposite sides of the winding leg so that coils mounted on the winding leg or bar will be positioned in the windows. Extensions may be provided to separate adjacent windows and form shunts.

The shell type core is usually formed of stacks of laminations in which those laminations stacked to provide the central winding leg have been punched out or" the center of laminations which thereafter form the framing portion. The material punched out to form the windows is scrap, which is quite substantial in the shell type core. Obviously scrap increases costs and ultimate prices to consumers.

The invention herein also utilizes a shell type core but not of the construction in which the frame portion is an integral member, that is to say an unbroken member formed of a stack of rectangular one piece laminations. The primary object of the invention is to provide a core construction of shell type made up of laminations so formed and shaped as to produce an extremely small quantity of scrap, while providing a highly effective, electrically and magnetically efficient transformer core.

The invention contemplates the mating formation of parts which will be assembled in stacks out of continuous electrical steel strips running at high rates through automatic stamping machines. In other words, the parts of each laminated layer of the core are so arranged along a continuous uniform width strip that the scrap is minimized.

It is understood that the mere mating arrangement of laminations or parts of laminations along electrical steel strips to decrease total scrap generally has been known, but where special requirements demand the provision of shunts in the core, scrapless mating of parts has not been accomplished to any practical degree. Even where scrap of some quantity is expected, known structures have not achieved the highly economical core of this invention and this accomplishment is another object of this invention.

The novel core of the invention is made up of several parts, comprising the central winding leg or bar, and two outer elongate members which are disposed on opposite sides of the winding leg and clamped thereto and proatet 'vide the framing portion. The assemblage can be considered a unitary structure because of the abutting joints between the outer members and the winding leg or bar, but obviously the same is not integral and according to the invention is not so constructed.

The invention resides in the provision of a core structure formed of T and L shaped parts forming the shell. The difference between this and prior structures, inter alia, lies in the fact that although the parts are arranged matingly along the strip from which the same are punched, the extensions which will form the shunts in the assembled core are integral with the parts so that there is no need to insert separate shunts. One form of the invention, which is especially economical, utilizes parts which are formed in such a manner that the central winding leg will have indentations from the punching out of the extensions of the side parts, but such indentations are positioned at a part of the transformer where their eifect upon the efficient operation of the transformer is practically unnoticed.

Many objects and advantages will occur to those skilled in this art as a detailed description of specific and preferred embodiments of the invention is set forth hereinafter, in connection with which illustrations are provided for clarity and to aid in an understanding of the invention.

In the drawings, in which the same characters of reference are used throughout the several figures in order to designate the same or similar parts:

FIG. 1 is a diagrammatic top plan view of a transformer constructed in accordance with the invention, and using the novel core of the invention, the coils being shown in section in order better to illustrate the details.

FIG. 2 is a fragmentary top plan view of a strip of electrical steel showing the lay-out of the parts of the core of FIG. 1 along the same to illustrate the small amount of scrap resulting from the core structure.

PEG. 3 is an electrical diagram of the circuit of the apparatus with which the transformer of FIG. 1 is intended to be used.

FIGS. 4 and 5 illustrate diiferent layouts along strips of electrical steel for a slightly modified form of the invention, but in which there is slightly more scrap resulting.

FIG. 6 is another illustration of a layout of parts of a core along a steel strip, the view being quite similar to that of FIG. 2, but the form of the invention being substantially identical to that of FIGS. 4 and 5.

Looking first at FIG. 1, there is illustrated a transformer it which is formed of a so-called iron core 12 which shortly will be described in detail. The transformer M is intended to be connected into a circuit for igniting and operating two gaseous discharge devices in a manner illustrated in F IG. 3. There the transformer core is shown to mount four windings comprising a primary winding P connected across a relatively low voltage A.C. line 14, a first secondary winding S which is spaced from the other windings along the core 12 and separated therfrom magnetically by means of a shunt 16, a second secondary winding S and an extension of the second secondary winding which is designated S The windings are connected end to end in order named, but the physical placement on the core 12 is otherwise. The first secondary winding S is disposed on the left hand end of the core 12 as viewed in FIG. 1, and the second secondary winding S is disposed on the right hand end. The primary winding P is in the center of the core and alongside the winding S and separates the winding S from its extension S As shown in the circuit diagram of FIG. 3, there is a gaseous discharge device such as a fluorescent lamp L connected in series with a condenser C and together therewith connected across the winding S There is a n all) second lamp L which is connected across all of the windings. In operation, the lamp L lights first after which the lamp L lights, and, by virtue of the placement of the winding S and the shunt 16, current principally flows in series through the lamps and the windings S and S and the condenser C. The exact manner of operation is described in U.S. Letters Patent No. 2,633,243 of A. E. Feinberg, one of the applicants herein.

It will be seen that the construction of the core ltl is such as to accommodate the windings described, provide the necessary shunt, and the air gaps and magnetic structure. This is done in the invention, without losing any of the advantages accruing by virtue of the highly economical construction of the core and the formation of the laminations thereof from strips of steel in the manner described in detail hereinafter.

The core 12 is formed of three stacks of laminations held together in any suitable manner by clamps or other fastening devices which are well known and need not be shown. There is a T-shaped central winding leg or bar 2%, the cross head 22 of which is shown at the right hand end in FIG. 1 forming the bridging magnetic connection of that end. Spaced inwardly of the right hand end there is provided a slot 24-, the purpose of which is to improve wave shape in the manner described in Paul Berger application for Letters Patent Serial No. 503,163 filed April 22, 1955. There is also a pair of identical side legs 26. These side legs or parts are L-shaped with the short leg 23 of each facing inwardly abutting the left end of the central winding leg or bar on opposite sides thereof and making magnetic connection therewith at 39. The right hand end of the side legs 265 meet the outer ends of cross head 22 in similar abutting joints 32.

The windings described are mounted along the central winding leg or bar 2% in the order also set forth, and the shunt 16 is disposed between the windings S and S The shunt ll'ti is formed by means of the inwardly extending lugs 34 integral with the side legs 26 and 27. The ends of the lugs are spaced from the sides of the central winding leg by some predetermined amount in order to provide the usual air gaps 35 of such shunts.

Attention is invited to the recesses 38 which are provided in the central winding leg 2@ between the shunt 1d and the left hand end of the core 12. These recesses are completely covered by the first secondary winding S which is the high leakage reactance winding of the apparatus, and which carries very little current, compared to the other windings of the transformer ll'lP, once the lamps are ignited. It has been found that positioning the recesses beneath the coil of the winding S prevents the leakage which might be caused by such a recess from producing noise in the cannister containing the apparatus. Also, since this winding will carry little current during the operation of the lamps, the effects of high flux density on wave shape caused by an effective narrow cross section of the central winding leg are substantially reduced.

Since the adverse effects of the recesses 38 are tolerable because of the nature of the operation of the transformer, it is possible to produce the parts of the transformer core 12 very economically.

In order to avoid confusion herein, the same characters of reference will be used to designate the stacked parts of the core 12 and the individual laminations used to make up such stacks. Thus, in FIG. 2 which shows a single thickness of a steel strip having parts of laminations laid out thereon, the reference character 26 designates a lamination intended to be combined with identical laminations in a stack to form the T-shaped central winding leg 20. Likewise the individual stampings 26 will be used to make the side legs 21'.

The strip of electrical steel id has the parts 20 and 2,6 laid out thereon in groupings of two side legs and one central winding leg disposed thcrebetween. The central winding leg part 20 however is shifted to the right relative the side legs 26 when compared with the eventual position in the assembled core. Thus, the side leg parts of each group are laterally closer together and the end of the central winding leg is abutted against the inside of the short legs of the side legs at 42, with the cross head 22 outside the right hand end of the side legs 26. The extensions 34 are punched out of the body of the central winding leg parts 2% giving rise to the recesses 38 referred to above.

With the layout described the amount of scrap is extremely small. All scrap areas in the drawings are shaded and marked S to identify the same, and it will be seen that the areas of FIG. 2 are quite small. There is one area 45 and an area 46 for every group of parts. The groups are arranged side by side with the backs of parts 26 abutting along lines ,3.

When the parts are stacked and assembled, the central winding leg 2% is shifted to the left, the side legs 26 being spread to accommodate the same, resulting in the structure of FIG. 1 which provides the necessary windows for the windings.

In certain structures it might be disadvantageous to have the recesses 38, and hence the layout of parts is somewhat different. In FIG. 6 there is illustrated a fragment of a strip 5% of steel, in which the central winding leg part 2% is shifted to the right compared to the layout of PEG. 2 so that it abuts against the side of the extensions Thus all of the strip which is contained between the side legs 26 and to the left of the end of the winding leg 2-3 is scrap, designated 52. Likewise, since the cross head 22 protrudes considerably beyond the ends of the side legs 25, there will be an additional irregular scrap area 54 between each group of parts. The side legs 26 are back to back along the line The strip 56" will obviously be wider than the strip dd and the amount of scrap from the layout of FIG. 6 greater than from the layout of FIG. 2.

In FIGS. 4 and 5 there are illustrated the layouts for parts along steel strips 56 and 58 for forming the winding leg parts 20' and the side leg parts 26 separately, instead of in the same operation as described hereinabove. In FIG. 4 the winding leg parts 2 are formed side by side and with heads alternately reversed to give rise to a single scrap area as for each part. In FIG. 5 the pairs of side legs 26 are laid out for punching with the short legs 28 and extensions 3d facing but the ends reversed so that there is mating of the parts and a minimum of scrap. The pairs are back to back. Each pair produces two irregular scrap areas 62 of the same size.

It is believed that the invention should be obvious without further description, and it is desired to point out that variations in details are possible without departing from the scope as defined in the claims. The structure shown in the drawings was used in constructing apparatus which gave successful results when used with two 75 watt instant start fluorescent lamps. The width of the central winding leg was approximately l /s inch and the other dimensions proportional.

The details of windings are as follows:

Primary winding P 550 turns #22 wire. First secondary winding 8 4100 turns #32 wire. Second secondary winding S 2000 turns #28 wire. Extension winding S 625 turns #28 wire.

The two windows accommodate all windings, with the winding S being 1.8 inches long, and the other three combined being a total of approximately 5 inches in length. The condenser C was 1.74 microfarads.

Although not illustrated, in addition to the scrap which is shown in the accompanying drawings, there may be a very narrow strip which is called a carrying strip alongside any of the wider strips illustrated for the purpose of supporting the partly punched laminations during progressive movement through the die. The use of carrying strips is a technique well known in the art. In addition, although not illustrated, the corners of the side parts 26 may be notched for the seating of clamps. This also is known and need not be illustrated.

What it is desired to secure by Letters Patent of the United States is:

1. Atransformer core of the shell type which comprises a central winding leg and two elongate side parts assembled thereto, the said winding leg and side parts being formed of stacks of laminations of mating edge configuration to enable substantially scrapless formation thereof, the central winding leg being of elongated T- shaped formation and the side parts of elongate L-shaped formation, the short legs of the side parts extending toward one another and being abutted against the end of the central winding leg opposite the cross head, and the said cross head of the central winding leg being abutted against the inside edges of the long legs of said side parts adjacent the ends thereof whereby the longer legs of the side parts and the central leg of the winding leg are parallel and spaced apart to form winding windows, a pair of integral lugs one on each of said side parts extending inwardly toward said winding leg to provide magnetic shunt means between windings adapted to be disposed in said windows on opposite sides of said lugs, a pair of recesses in said winding leg, one each on opposite side edges thereof of configuration substantially identical with the configuration of said lugs, and each recess having an edge spaced from the conforming edge of its adjacent lug along the length of said winding leg by substantially the width of said cross head, and being wholly contained within the length of one window whereby that winding adapted to be disposed within said one window will cover the recesses.

2. In a ballast structure for igniting and operating at least one gaseous discharge device from a source of AC. power and in which the ballast structure includes an iron core transformer having a primary winding and at least one secondary winding, in which the core has a shunt between the primary winding and said secondary winding to provide a substantial amount of leakage reactance when said ballast structure is operating, in which the primary winding is adapted to be connected across the source and the windings are adapted to be connected in circuit with the said gaseous discharge device, the herein invention which comprises: the transformer including an elongate shell type core formed of three stacks of laminations secured together, comprising a central T-shaped winding part having an elongate central bar and an integral cross head, a pair of substantially L-shaped side parts, each side part having an elongate leg and an intergral short leg at right angle thereto at an end thereof, the primary and secondary windings being mounted on the central bar of the T-shaped part, the short legs of the side parts being abutted against the opposite side edges of the central bar opposite its cross head, the ends of the cross head being abutted against the respective side edges of the elongate legs of the side parts at their ends opposite the short legs, the central bar of the T-shaped part being parallel with the said elongate legs and equally spaced from each of said elongate legs to cooperate therewith to form windows for said primary and secondary windings in said core, each side part having an integral lug formation between its ends identically located and extending toward the central bar but terminating short thereof to provide a gapped shunt, and the primary and secondary windings being located on opposite sides of said shunt respectively but with at least said secondary winding adjacent said shunt, the central bar having a pair of recesses therein on the side edges thereof identically located and disposed beneath said secondary winding and of substantially the same configuration as said lug formations, and each part of the recesses being spaced along said central bar from the corresponding part of said lug formation on the same side of said central bar by substantially the width of the cross head, to provide a reduced area portion of said central bar beneath said secondary winding, the facing edges of the side parts and central T-shaped winding part being of mating configuration, although the side parts are assembled spaced from said central part and disposed in translated relation thereto, but enabling the laminations forming said parts to be cut from sheet metal with a minimum of scrap.

3. In a ballast structure for igniting and operating a gaseous discharge device and having primary and secondary windings connected with said device, said windings being mounted in windows in an iron core; the herein invention comprising a core structure of the shell type having a central winding-mounting member of generally T-shaped configuration and a pair of elongate side members of generally L-shaped configuration cooperating with said central winding-mounting member in a unitary assemblage to form said shell, the central winding-mounting member being formed of individual laminations of ferromagnetic material of identical T-shaped configuration stacked and secured together, the side members being formed of individual laminations of ferromagnetic material of identical generally L-shaped configuration stacked and secured together, the L-shaped side members being arranged on opposite side edges of the T-shaped central member with the short legs of the L-shaped members engaged in abutting relationship with the longer leg of the T-shaped member and the ends of the cross head of the T-shaped central member engaged in abutting relationship with the longer legs of the L-shaped side members, thereby forming the bridging end parts of said shell, the longer legs of the L-shaped members being parallel with and equally spaced from the opposite side edges of the longer leg of the T-shaped member to provide winding windows on the interior of the shell, the longer leg of each L-shaped side member having an identical integral lug formation extending inwardly toward and terminating short of the opposite side edges of the longer leg of the T-shaped member, the primary and secondary windings being mounted in said windows and separated by said lug formations whereby said formations comprise a magnetic shunt between said primary and secondary windings, the side edges of the longer leg of the T-shaped member being of configuration complementary with the respective facing side edges of the L-shaped side members, considering those edges included between the inside of the cross head and end of the T-shaped member and those edges included between the inside of the short legs of the L-shaped side members, albeit the L-shaped members are spaced from and translated lengthwise of said T-shaped central member, there being formed thereby a pair of recesses in the side edges of said long leg of the T-shaped member of configuration identical to the configuration of said lug formations but spaced therefrom along the length of said shell, said windings being mounted with the secondary winding covering said recesses, and said recesses thereby providing a reduced cross section of said T-shaped winding leg beneath said secondary winding.

4. A structure as claimed in claim 3 in which there is a capacitive reactor connected in circuit with said windings and device but being in series with said secondary winding.

5. In a ballast structure of the character described, comprising, an iron core of shell type having a central winding leg, side parts and bridging ends, Winding windows formed between the central leg and the side parts, at least a pair of windings disposed on the winding leg along its length and occupying the windows, one window of said pair comprising a primary winding adapted to be connected to a source of A.-C. power, the other winding of said pair comprising a secondary winding and adapted to be mounted on said central leg at a position where the cross section of the central leg has been substantially reduced, a magnetic shunt between said windings, at least one gaseous discharge device connected to be energized by said windings, and a capacitive reactor in series with the said secondary winding, the herein invention which comprises: a core structure adapted to be formed from substantially scrapless nested laminations Of T and L configuration of the same respective overall length, the central winding leg comprising a stack of identical T-shaped laminations, the side parts each comprising a stack of identical L-shaped laniinations, the central winding leg being arranged with the cross head of the T abutting the long legs of the side parts to form one briding end, the short legs of the L-shaped side parts abutting the side edges of the end of the long leg of the T-shaped central leg to form the second bridging end, an integral lug extending from each of the side parts toward the central winding leg to form said shunt, and the windings being located on opposite sides of said a shunt, a pair of recesses in opposite side edges of the central winding leg of configuration identical to that of said lugs and spaced therefrom at one side of said shunt, and the secondary winding being mounted on said central winding leg to enclose said recesses whereby said recesses provide said reduced cross section, the longer side edges of the central leg and side parts being of complementary configuration.

References Cited in the file of this patent UNITED STATES PATENTS 2,558,293 Feinberg June 26, 1951 2,824,263 Strecker et al. Feb. 18, 1958 2,827,615 Henderson Mar. 18, 1958 2,907,966 Dierstein Oct. 6, 1959 

